The modern household can be a chaotic place, full of noise from televisions, computers, and playing children. This proposal comprises two sets of studies that, taken together, will greatly enhance our understanding of how infants learn language in such an acoustically hostile environment. These studies investigate both how infants disentangle the speech of different talkers speaking simultaneously, and how much experience they need in order to then separate that fluent speech into individual words. Most research on infant language acquisition has taken place in quiet laboratory rooms with no outside distractions, but in the real world, speech directed to infants often occurs in the presence of competing acoustic signals. Most current theories of language acquisition suggest that children "bootstrap" their way into language comprehension by exposure to large amounts of language information. Infants' ability to separate speech from background noise limits the amount of this information they can use. Thus, studying these basic attention abilities provides an important underpinning for theories of language acquisition. In addition, understanding the degree to which infants are affected by background noise is relevant in evaluating child-care decisions, as settings involving greater numbers of children are likely to result in greater degrees of noise. If infants have difficulty selectively attending to a caregiver in noisy situations, infants placed in quieter environments may have an advantage in learning language. The first set of studies examines how infants learn language in non-ideal environments. Recent research has shown that infants, like adults, have the ability to separate streams of auditory information (Newman and Jusczyk, 1996). Little is known about the limits of this ability, however, and the studies described here examine this more fully. A second set of studies investigates the amount of exposure to language an infant requires to begin the language-learning process. Many theories assume infants need linguistic experience to pick out individual words from fluent speech, but how much experience is required remains unclear. The present studies explore this issue, as well as whether infants can learn language from non-interactive situations, such as watching television. These studies further explore the role of early attentional and segmental mechanisms on language development, with the goal of constructing a theoretical model of infant language acquisition, one which is grounded in a better understanding of the problems infants face outside of the laboratory.